Many studies have been made by various research institutes on a collector including a carbon-based conductive substance that is applied onto a metal foil such as an aluminum foil or a copper foil used as a substrate of an electrode for a secondary battery. In addition, there have been many patent applications including, for example, PTL1 to PTL4.
PTL1 and PTL2 each describe a collector including a substrate such as an aluminum foil or a copper foil and a coating provided on a surface of the substrate, the coating being formed of fine carbon particles (conductive substance) as conductive substance and a coating-forming compound. PTL3 describes a collector including a conductive layer between the collector and an active material, the conductive layer being formed of carbon powder (conductive substance) and a binder. PTL4 describes a collector having a conductive coating layer on its surface, the conductive coating layer including carbon as a conductive agent. Such techniques are intended to reduce contact resistance between the collector and an active material layer formed on the collector in order to improve high-speed charge-discharge characteristics and cycle characteristics of a battery.